The present invention relates to ophthalmic lens systems and, in particular, to ophthalmic lenses that attenuate the transmission of high energy visible light.
Only a small portion of the electromagnetic spectrum is of concern to the human eye. This portion of the spectrum lies in a range of wavelengths from about 100 nm to about 700 nm, and can be divided into several discrete groupings—ultraviolet (UV) light, high energy visible (HEV) light, and low energy visible light. UV light ranges in wavelength from about 100 nm to about 400 nm, and is subdivided into 3 regions—UVC (100 nm to 280 nm), UVB (280 nm to 320 nm), and UVA (320 nm to 400 nm). HEV light ranges in wavelength from about 400 nm to about 500 nm, and generally corresponds to the blue (or blue-violet) region of the visible spectrum. The last region that is of consequence to the human eye is low energy visible light, which ranges in wavelength from about 500 nm to about 700 nm.
It is widely known that UV light is harmful to the eye. UVC is completely blocked by the ozone layer, which also blocks most of UVB. Consequently, about 95% of the UV light from the sun consists of UVA. There is also a growing body of research indicating that HEV light from 400 nm to 500 nm can cause damage to the eye and in particular the retina. Although the lens and cornea of the human eye blocks UVB and most of UVA, virtually all of the HEV light can penetrate the lens and impact the retina at the back of the eye.
HEV light affects the eye in multiple ways. HEV light has been implicated in Age related Macular Degeneration (AMD), which is the leading cause of progressive blindness in seniors. One of the causes of AMD appears to be damage to the retinal pigment epithelium (RPE), a layer of light sensitive cells that lie behind the photoreceptors in the retina which are responsible for vision. Although the exact pathology of AMD is not completely understood, there is growing evidence that the exposure to HEV light may play an important role in damaging RPE cells and the development of AMD.
HEV light is also thought to contribute to eyestrain and to reduced visual acuity under certain conditions. The short, high energy wavelengths associated with HEV light may cause blue light to flicker and create glare more easily than longer, lower energy wavelengths. As a result, prolonged exposure to HEV light (e.g., from computer screens and energy efficient lighting) may cause eyestrain, headaches, physical and mental fatigue. In addition, the axial (longitudinal) chromatic aberration of light through the crystalline lens of the eye can create a “blue light blur”. FIG. 1 shows light of different wavelengths 4, 5, 6 passing through the lens 3 of an eye 2. The different wavelengths are refracted differently and focus at different distances from the lens. Blue light refracts more than the other wavelengths, resulting in a focal point 7 of blue light in front of and not on the retina 8. This effect may be observed as a blue haze around objects in bright light (e.g., sun and snow), and also in foggy conditions where blue light is strongly reflected. In addition, fluorescent lamps and LED lighting (e.g., automobile headlights) have significant output of HEV light and can similarly contribute to a loss of visual acuity, especially at night while driving. Thus, the growing ubiquity of blue light from computer displays and other electronic devices, modern lighting, and other sources makes the management of HEV light a matter of growing importance.
Notwithstanding the problems associated with HEV light, visible light between about 460 nm to about 500 nm is a regulator of the circadian response in humans. Therefore, it would be desirable to reduce exposure to HEV light and, in particular, reduce eyestrain and blue light blur, without significantly affecting transmission of light in the range from about 460 nm to about 500 nm so as to not inhibit the natural function of the circadian cycle.